Measuring apparatus



Patented 3,1946

MEASURING APPARATUS John R. Woodyard, Garden City, N; Y., assignor to Sperry Gyroscope Company, Inc., a corporation of New York Application June 28, 1943, Serial No. 492,573

My invention relates to electrical measurin devices in general, and more particularly to methods and apparatus for determining the phase an gle'between two alternating or periodically vary ing quantities.

An object of my invention is to provide a device for measuring the phase difference between two periodically varying quantities in which the restoring force acting on the indicating element thereof is independent of frequency.

Another object of myinv ention is to provide an electronic phase meter which is less affected by noise or other random fluctuations than are .prior electronic phase meters.

It is also ancbject of my invention to provide a phase meter which utilizes the information of the impressed signal quantities over whole cycle periods.

Another purpose of my invention'is to provide a method and apparatus forv determining the phase angle between two alternating electrical quantitiesin which a product of the two is divided by another product, obtained by multiplying the two quantities after rectification, to give a measurement of phase difierence.

Another purpose of my invention is to provide a phase meter in which no moving parts carry the quantities whose phase difierence is to be measured. I

A still further object ofmy invention is to arrange in an electronic phase-measuring circuit two balanced modulators, which produce direct current outputs respectively proportional to a function of the phase angle between the two quan- .tities whose phasedifierence is to be determined and to their product, and a device such as a crossed-coil ohmmeter which is capable of taking the quotient of the two direct currents so produced, to give an indication of the phase angle.

Yet another purpose of my invention isto provide a method for determining the phase angle between two periodically varying electrical quantitles in which two direct currents are produced therefrom by modulation and rectiflcatio which 11 Claims. (01. 172-245) nating quantities is modulated with the other to produce a direct current proportional to a function of the phase angle between them.

The alternating quantities are rectified in another branch of the circuit by means of full-wave rectifier-s and impressed on the signal and carrier terminals of a second balanced modulator, the output of which is proportional to the product or the two periodically varying quantities. The outputs of each of the balanced modulators are then delivered to a quotient-taking device where the quotient of the two modulated outputs is taken to give an indication of the phase angle to bedetermined.

' A more comprehensive understanding of my invention will be afforded from the following detailed description when taken together with the accompanying drawing in which, d

Fig. 1 is a circuit diagram of an embodiment of my invention;

Fig. 2 is a modified block diagram of the cirf cuit shown inF-ig. 1; and

Fig. 31s a schematic diagram showingthe operation of the balanced modulators used in Fig. 1. As indicated schematically in Fig. 2; the illustrated apparatus comprises a pair of balanced modulators l3 and 80, each of which is made responsive .to both of the vector voltages Eli and E2, which are to be compared in phase. The modulator I3 is directly connected to the voltage inputs E1 and E2 so as to yield an output proportional to the vector product of the input voltages, which includes the .phase angle factor, cos 0. On

. the other hand, the balanced modulator 60 has rectifiers 3i and 43, respectively, interposed in the inputconnections from the voltages E1 and E: so that phase-effect is eliminated and 'D.-C. voltages representing scalar values E1 and E: are supplied to the balanced modulator 60 rendering it responsiveto the scalar product of the voltages. The ratio instrument His provided, which has input connections from the output of the. elements i3 and 60 for producing a phase angle indication. v

, In the embodiment of my invention illustrated more in detail in Fig. 1, I provide two pairs of input terminals and II which receive the alter- 'nating quantities whose phase angles'are to be 5 compared.

From input terminals ll, the quantity impressed thereon is conducted to transformer 14 whose tapped secondary forms the balanced circuit of balanced modulator i3; comprising the electronic discharge devices i1 and I8, illustrated input terminals the electrical quantities are delivered to the'signal and carrier input terminals of a balanced modulator where one of the alteras triodes.

Transformer IS; the secondary of which is coupled in the cathode circuit of balanced modu-- lator l3, receives the electrical quantity impressed upon input terminals I2.v Controlv grids i9 and .former l5.

' 24 of elements 11 and I8 receive signal voltages 1 these elements form a circuit for connecting cathodes 22 and 23 of elements 11 and 18 to the mid-point of the secondary winding of transformer l4.

Plates 2| and 25 of these elements deliver the output of balanced modulator 13 to resistors 29 and 30 and receive positive voltage from source 28. By-pass capacitors'26 and 21 are coupled in parallel with elements 11 and I8, respectively, for by-passing the alternating components of their respective outputs.

The signal received on input terminals H is also delivered to the primary winding of transformer 32 which, together with the electronic discharge elements 33 and 34, comprises the fullwave rectifier 3i. Anodes 35 and 31 of elements 33 and 34, both of which are illustrated as diodes, receive the output of the secondary winding of transformer 32 and their cathodes 36 and 38 deliver the output of the rectifier to a filtering circuit comprising a resistor 39 and capacitors 4| and 42. The output of full-wave rectifier 3| is delivered to the signal input terminals of balanced modulator 60, which in turn delivers it to the control grids 62 and 66 of elements 59 and comprising a part of balanced modulator 60.

The electrical quantity received on the input terminals l2 passes through the primary winding of transformer 44 and is induced in the secondary winding thereof for delivery to anodes 41 and 49 of elements 45 and 4B in the full-wave rectifier 43. The output of this last-mentioned device is taken from cathodes 48 and 5| and delivered to a filtering circuit comprising capacitor 52, resistor- 53, and capacitor 54. Throughthe filtering circuit last mentioned the output of the full-wave rectifier 43 is delivered to the balanced modulator 50 across the resistor 51.

The output of balanced modulator 60, in the form of a direct current proportional to E1E2 is delivered from plates 63 and 61 of elements 59- and 5| to the resistors 12 and 13. 'Plate current is supplied the elements of balanced modulator 60 from source 1| and the grids thereof are biased from voltage source 58. By-pass capacitors 68 and 69 are coupled in the output circuit of balanced modulator 60 for by-passlng A. 0. components.

The direct current outputs of balanced modulators I3 and 60 are delivered to a quotient-taking device 14, which is illustrated. as a crossed-coil ohmmeter and which is calibrated to give an indication of the phase angle existing between the two voltages impressed upon input terminals II and I2.

While element 14 is illustrated as a crossed-coil ohmmeter it may take the form of any ratiometer or quotient-taking device, such as an Evershed Meg'ger, or may be of the electronic type in which electronic discharge-elements having logarithmic characteristic curves are used.

With reference to Fi 2, the operation of the circuit may be explained from a functional stand- .point in the following manner:

The vector quantity 1 11 representing one of the two alternating quantities, between which the phase angle difference is to be determined, is received by balancedmodulator l3 where it modulates the quantity 112 to produce a direct current output proportional to the quantity E1E2 cos 0.

Within the rectifiers 3| and 43, each of the respective quantities are rectified to produce scalar quantities E1 and E2 which are delivered to balanced modulator 60 operating as a product-taking circuit. The output of this last-mentioned circuit, proportional to the product ElEZ, and the current proportional to the product EIEZ cos 0, are delivered to a quotient-taking device 14 where division of the two quantities is made to give an indication of 0.

In operation, the balanced modulators l3 and and the plate current i2 of tube l8 as Where the as are constants, the value of each depending upon tube characteristics and external circuits, and ea and er are the instantaneous values of signal and carrier voltages respectively, whose values may be expressed as (3) 8a==Ei sin wt and (4) 8b=E2 sin (wt-9) where 6 is the phase angle between E1 and E2.

The resultant current it delivered to terminals 15 and 16 is therefore equal to the algebraic sum of the currents i1 and i: or

which in terms of Equations 1 aid 2 may be expressed as By choosing the'proper operating voltages for the tubes 11 and i8, all components higher than the second order will be made negligible and Substituting the values of es and en, expressed by Equations 3 and 4, in Equation 8 and collecting terms and is proportional to EIEZ cos 0. 4

By similar analysis as evidenced by Equation 9 developed above, it is seen that the output iudc iode=2d2E1E2 cos 0 of balanced modulator is proportional to the product EiEz, and when combined by suitable means with the output of balanced modulator i3, expressed by Equation 10, a quantity proportional to cos is obtained and through propertrical quantities, comprising means for modulating one of said quantities with the other, means for rectifying each of said periodically varying quantities, means for modulating said rectified electrical quantities one with the other, and means for receiving the outputs of the respective modulating means to give an indication of-phase.

2. In an electronic phase meter, a first balanced modulator for modulating one of two periodically varying electrical quantities with the product of said periodically varying electrical quantities, means for rectifying each of said .termlnals for respectively receiving first and other, separate rectifiers for rectifying each of said periodically varying quantities, a second balanced modulator for modulating the output of one of said rectifiers with'the output of the 6 trical quantities varying in phase with each other by an angle 0, means for producing from said alternating electrical quantities a first direct current proportionalto a function of said angle 0, means for producing from said alternating electrical quantities a second direct current proportional to their-product, and means for taking the quotient of said first and said second direct currents to give an indication of the value of said angle 0.

7. A method for measuring the phase diiference between two alternating electrical quantities, comprising the steps of modulating one of said quantities with the other to produce a-product thereof, converting each of said alternating of said products so produced to give an indi cation of phase angle.

8. A method of measuring the phase angle between two periodically v'aryi'ngelectrical quanother, and means for determining th quotient of the outputs of said first and second modulators to give an indication of phase angle.

3. In an electronic phase meter a circuit having wo pairs of input terminals each of which re-. ceive one of two periodically varying electrical quantities, a balanced modulator for modulating one of said quantities with the other, first and second full-wave rectifying devices for rectifying each of said periodically varying electrical quantities, a balanced modulator-for modulating the output of said first full-wave rectifier with the output of said second full-wave rectifier, and means including a crossed-coil ratiometer for receiving the outputs of said balanced modulators to give an indication of the phase angle between the two quantities impressed on terminals of the circuit. 4. Apparatus for measuring the phase relationthe input ship between two periodically varying electrical v quantities, comprising means for taking the periodically varying electrical quantities to produc a plurality of rectified outputs, means for taking the product of said rectified outputs, and means for dividing one product by the other to measure the phase angle between said periodically varying electrical quantities. i

5. An electronic circuit comprising a first haltitles, comprising the stepsv of multiplying one with the other to obtain a first product, rectifying each of said periodically varying electrical quantitles to produce two unidirectional quantities, multiplying one of said unidirectional quantities with the other to produce a second product, combining said first and second products to produce an electrical quantity proportional to the phase angle between the two periodically varying electrical quantities, and measuring said last-mentioned electrical quantity to give an indication of phase angle. 4

9. A method for determining the difference in phase between'two alternating electrical quantities, comprising the steps of modulating one of said quantities with the other to produce a first modulated quantity, rectifying each of said alternating electrical quantities to produce first and between two periodically varying electrical quananced'modulator having'signal and carrier input and means for dividing the output of said am balanced modulator by that of saidsecond balanced modulator to .give an indication of the angle 0.

6. An electronic phase determining device comprising means for receiving two alternating electities, comprising the steps of producing a first direct current from said periodically varying electrical quantities proportional'to a function of the phase angle between them, producing a second direct current from said periodically varying electrical quantities proportional to their product, and taking the quotient of said first and second direct currents to .give an indication of phase angle.

11. A method of measuring the phase relationship between two periodically varying electrical quantities, comprising the'steps of modulating one of said periodically varying electrical quantitles with the other to produce a first modulated quantity, rectifying each of said periodically varying electrical quantities to produce two nonperiodically varying electrical quantities therefrom. modulating one of said non-periodically varying electrical quantities with the other to produce a second modulated quantity, and combining said first and second modulated quantities to give an indication of phase angle.

' JOHN R. WOODYA RD. 

